1. Field of the Invention
The present invention relates to numerical controllers, and particularly relates to a numerical controller capable of controlling acceleration and deceleration along each axis so as to avoid damaging touch probes and reduce shock received by a machine tool.
2. Description of the Related Art
In machine tools, measuring the shape of a measurement target such as a workpiece is extremely important for high-accuracy machining. A technique that measures the shape of a measurement target by bringing a tip of a touch probe into contact with a surface of the measurement target has been known as a technique for measuring the shape of a measurement target.
In a measurement method according to this conventional technique, the touch probe is supported in a mobile state by a drive axis, and the shape of the measurement target is measured on the basis of the positions of the drive axis where the tip of the touch probe contacts the measurement target.
Meanwhile, a technique for a controller of a machine tool has been disclosed, in which the tangential velocity of a tool is controlled in accordance with a permissible maximum acceleration set for each axis so as to achieve acceleration and deceleration control that makes full use of the acceleration performance of each drive axis in a machine tool (Japanese Patent Application Laid-Open No. 11-338530, for example).
When measuring the shape of a measurement target using touch probes, a signal is generated upon the touch probes contacting the measurement target, and the touch probes are stopped by a numerical controller that receives the signal carrying out stopping control on the drive axis that supports the touch probes in a mobile state. Here, there is a problem in that the touch probes will be damaged if the touch probes are not stopped within a predetermined distance after contacting the measurement target.
However, even when the technique disclosed in Japanese Unexamined Patent Application Laid-Open No. 11-338530, for example, is used to control the axis movement at the permissible maximum acceleration, there are situations where the touch probes cannot stop within the predetermined distance after a stopping command has been issued, resulting in the touch probes being damaged. While a method that sets the permissible maximum acceleration to a high value is conceivable as a way to avoid such situations, using such a setting method results in the drive axis always stopping at an acceleration that is as close to the permissible maximum acceleration as possible. As such, although this method does shorten the stopping distance and avoids damage to the touch probes, the method also increases shock imparted on the machine tool when stopping, resulting in a problem in that a heavy burden is placed on the machine tool.